In one of known types of inkjet printing apparatuses ejecting ink from a print head onto a print medium, ink is ejected during the movement of the print head across the print medium in order to print an image. Another type of inkjet printing apparatus prints an image by ejecting the ink from the print head while moving the print medium relative to the print head that is fixedly mounted.
Some methods for supplying ink to a print head which are employed in such inkjet printing apparatuses will be described below. One of them is the so-called “on-carriage method” in which ink is supplied from an ink tank that is attached integrally with or detachably to the print head which is mounted on a carriage or the like so as to reciprocate. Another method is the so-called “tube supply method” in which ink is supplied from an ink tank that is fixedly placed in an area of the printing apparatus independently of the print head mounted on the carriage and is fluidly connected to the print head through a flexible tube or the like. In the case of the “tube supply method”, there is also a form of mounting a second ink tank for retaining the ink on the print head or the carriage between the ink tank and the print head.
In the inkjet printing apparatuses as described above, a mechanism for generating negative pressure is provided in the ink tank in order to prevent ink leakage from a print head nozzle. The mechanism can take the form of providing a porous member in the ink tank for retaining the ink and using the ink retaining force of the porous member impregnated with the ink to generate negative pressure. In another form, a bag made of a material having an elastic force such as rubber is filled with ink. Negative pressure is generated in the tank by causing a tension to act on the bag in the external direction.
In another known form, negative pressure is generated by using a spring or the like, provided inside or outside an ink storage portion formed of a flexible sheet, to urge the sheet member in a direction of expanding the sheet member. In some ink tanks employing the sheet member, a part of the sheet member is shaped in a protrusion form in order to contain a larger amount of ink. By use of the ink tank of this form, an inkjet printing apparatus improved in a print speed and an image quality is capable of supplying ink at a constant flow velocity and a flow rate, and also of using ink having various physical properties such as pigment ink.
When such an ink tank is used to supply ink to the print head, the structure of mounting a capillary member in a tank communication port is adopted in some cases as disclosed in Japanese Patent Laid-Open Nos. 08-132633 (1996) and 09-300646 (1997).
Next, the structure disclosed in Japanese Patent Laid-Open No. 08-132633 (1996) will be described.
The ink tank described in Japanese Patent Laid-Open No. 08-132633 (1996) comprises an ink storage portion and an intermediate chamber extending laterally from the bottom of the ink storage portion, and a capillary member provided in the ink storage portion. The ink tank has a negative-pressure generating mechanism which uses the capillary force of the capillary member to retain the ink. In addition, an ink supply portion is provided for supplying the ink from the ink storage portion to the outside of the ink tank. The ink supply portion is provided with a meniscus forming member having a great number of pores formed therein and a porous member which changes in volume between when the ink tank is attached and when it is detached. The porous member is formed of a material which changes in volume by a pressing force and has a high power of absorbing the ink, and formed in a tapered shape having a flat head.
The print head disclosed in Japanese Patent Laid-Open No. 08-132633 (1996) has an ink introduction portion connected to the ink supply portion of the ink tank. The ink introduction portion is provided with a sealing member placed in a position making contact with the outer periphery of the ink supply portion of the ink tank. Then, a filter is provided at an end of the ink path extending from the ink introduction portion to the ejection port. When the ink tank is removed, the porous member built in the ink supply portion is released from its compressed state approximately concurrently with the detaching of the ink tank, leading to an increase in the volume of the porous member itself and an increase in the porosity. As a result, an ink leak is prevented by the porous member absorbing the ink attempting to flow out of the ink tank which is being removed.
The basic structure of the ink tank disclosed in Japanese Patent Laid-Open No. 09-300646 (1997) is approximately the same as the structure of the ink tank disclosed in Japanese Patent Laid-Open No. 08-132633 (1996), but differs from it in that the ink supply portion is provided with a coupling capillary member, instead of the porous member. When the ink tank is mounted to the print head, the filter of the print head is in contact with the coupling capillary member of the ink tank. The coupling capillary member used has a higher density than that of the capillary member provided in the ink storage portion and generating a negative pressure in the ink tank.
However, in the ink tank described in Japanese Patent Laid-Open No. 08-132633 (1996), the porous member placed in the coupling between the print head and the ink tank widely changes greatly in volume and the entire porous member has a small force of holding the meniscus. In addition, the porous member is housed in the coupling between the joint portion and the ink introduction portion when it is in a uniform compressed state. For this reason, when the negative pressure in the tank increases during the operation using the ink tank, meniscus destruction occurs in the porous member during the operation, which may possibly cause air to be drawn toward the print head through the porous member. If the air is drawn into the print head, this makes it impossible to use up the ink, resulting in a reduction in the amount of ink available.
In the ink tank described in Japanese Patent Laid-Open No. 09-300646 (1997), if the contact area with the filter of the print head is smaller than the area of the coupling capillary member, even after the ink has run out, a portion of the ink remains in the coupling capillary member. As a result, the ink cannot be completely used up, leading to a possibility of a reduction in the efficiency of ink use.
In addition, the arrangement of an ink guide member in an ink supply port is known from Japanese Patent Laid-Open No. 2007-90873 which has proposed a combination of an enclosure, a flexible film and an elastic member used for generating a negative pressure to form an ink tank structured to directly store ink.
FIG. 13A and FIG. 13B are diagrams illustrating the ink supply portions of conventional ink tanks. These types of ink tank have an ink guide member 122 disposed in the ink supply portion. For example, in the structures disclosed in FIG. 13A, a thick ink guide member 122 is provided, and is in contact with an ink supply tube 151 while being mounted in a holder. This contact causes a compressed state of the ink guide member 122 particularly in the vicinity of a portion 122a making contact with the ink supply tube (that is, an area where the capillary force is relatively high), and a little-compressed state of a portion 122b of the ink guide member 122 on the side opposite to the contact area (that is, an area where the capillary force is relatively low and approximates one without compression). Then, as the ink is supplied, the negative pressure in the ink tank gradually increases. As a result, the area with a low capillary force is located between the ink tank and the ink supply tube, and it may possibly cause a situation that the ink supply path is split. This will make it impossible to fully draw the ink from the ink tank. In the structure illustrated in FIG. 13B, because a portion 122c around which the ink guide member 122 is located is strongly compressed, ink will remain in these portions.